Automatic telephone switching system



y 1952 H. cs. DuI-IAMEL. ETAL 2,604,539

AUTOMATIC TELEPHONE SWITCHING SYSTEM Filed April 5, 1948 11 Sheets-Sheet l Lm z eezow LIN2%%OUP 02$ I Q laj suaLINE m SLBLINE 1! cIRcurr cIRcurr toc'AILLINk cIRcuI'r /E8 FINAL sa e-010R /E5 4 TRUNK LINK 'T'NUNK LINK RC uncun' IE9 FINAL $ELEOT0R\ 3 {E 15 OIRCU|T REGISTER LINK 0a LINE FINDER m5 //07.; START REGISTER sum REGISTER cmcun LI NK cmcun LINK REGISTER 89 Y /08 SELECTOR ReIsTER* To FIG. I.

FIG 50. FIG 3b.

FIG. 6.

- INVENTORS l I HOWARD s. DUHAMEL I BY RAYMOND A. REED 7/ FIG. 46. ED 0. CAMPBELL A ONEY July 22, 1952 H. G. DUHAMEL ETAL 2,604,539

AUTOMATIC TELEPHONE SWITCHING SYSTEM Filed April 5, 1948 11 Sheets-Sheet 2 STATION LINE CIRCUIT I04 SELECTOR l/E' SELECTOR //5 GROUPS 3nvntors HOWARD G. DUHAMEL REGISTER LINK FIG. 3. RAYMOND A. REED EDWARD 0. CAM PBELL July 22, 1952 H. G. DUHAMEL ETAL 2,604,539

AUTOMATIC TELEPHONE SWITCHING SYSTEM Filed April 5, 1948 11 Sheets-Sheet a INVENTORS HOWARD G. DUHAMEL RAYMOND A. REED J 1952 H. G, DUHAMEL ETAL 2,604,539,

AUTOMATIC TELEPHONE SWITCHING SYSTEM Filed April 5,1948 1 1 Sheets-Sheet 4 INVENTO R5 HOWARD G. DUHAMEL July 1952 H. G. DUHAMEL ETAL 2,604,539

AUTOMATIC TELEPHONE SWITCHING SYSTEM Filed April 5, 1948 11 Sheets-Sheet 5 To FIG- INVENTORS HOWARD 6. DUHAMEL F'G. 3C. RAYMOND A. nsso BY EWAR O. CAMPBELL 7 Aozizv July 22, 1952 Filed April 5, 1948 FIG. 3d.

H. G. DUHAMEL ET AL AUTOMATIC TELEPHONE SWITCHING SYSTEM 11 Sheets-Sheet 6 INVENTORS HOWARD 6. DUHAMEL RAYMOND A. REED f apfgyao o. CAMPBELL z ATTOENEY y 22, 1952 H. G. DUHAMEL EI'AL 2,604,539

AUTOMATIC TELEPHONE SWITCHING SYSTEM Filed April 1948 v 11 Sheets-Sheet 7 3 HNVENTORS e. HOWARD e. DUHAMEL RAYMOND A. REED BYEQD 0. CAMPBELL July 22, 1952 H. G. DUHAMEL ETAL 2,604,539

AUTOMATIC TELEPHONE SWITCHING SYSTEM I Filed April 5, 1948 11 Sheets-Sheet 8 INVENTORS HOWARD G. DUHAMEL RAYMOND A. REED BY EDWARD 0. CAMPBELL FIG. 4b.

July 22, 1952 I H. G. DUHAMEL. ET AL 2,604,539

AUTOMATIC TELEPHONE SWITCHING SYSTEM Filed April 5. 1948 11 Sheets-Sheet 9 INVENTORS HOWARD G. DUHAMEL RAYMOND A. REED fiy/ZY ggWARD 0. CAMPBELL ORNEY y 1952 H. G. DUHAMEL ETAL AUTOMATIC TELEPHONE SWITCHING SYSTEM 11 Sheets-Sheet 10 Filed April 5, 1948 INVENTORS HOWARD c DUHAMEL RAYMOND A. REED y B! EDWfii D 0. CAMPEELL July 22, 1952 Filed April 5, 1948 u E: mu304 REED I- SW m mm EG NV W W 0 H IIIIIIIIII IIIIIIIIII I IIIIIIIIIIIIIIIIIIIIIIIIIII I III I iIllllllllI IIIIIIIIIIIILl-llllllll IIIIIIIIIIIIIII I I I I I I.|l |l INN |}|::||\w|:e::|M 1 -liilm llilllfl III I I l l as ||l|||||l||lll...|||||||.|||ll|.i|||||llllnlllllllllllnlull II I II I II I QR Illllll-III I I IIIIIIIII I IIIIIIIIII I I IIIIIIIIII I I I %& SE EN m8 Mm 3 2 Sm QR ORNEY Patented July 22, 1 952 AUTOMATIC TELEPHONE SWITCHING I SYSTEM Howard G. DuhameLVerona, N. J., Edward 0. Campbell, Flushing, N. Y., and Raymond A. Reed, Rutherford. N. -J., assignors to Federal Telephone and Radio Corporation, New York, N. Y.,acorporation of Delaware- Application April 5, 1948. Serial No. 19,026

This invention relates to new and useful improvements in automatic switching systems and is more particularly related to the register link and register circuits which receive the impulses from the subscribers dial and control the establishment of the desired connection in accordance with these impulses.

Anautomatic telephone system for use in small communities which employs register link and register circuits of the type to which this invention relates is fully described in co-pending patent application Serial No. 19,024 filed April 5, 1948, now abandoned.

In suchsmall community automatic systems, the call-number consists of four digits, the first three of which designate the line number which identifies the location of the line in the final selector terminal banks. The fourth digit designates the type of ringing current to be sent over the called line to a multi-party line.

According to one feature of the invention the digit pulses of the first digit of the call number are recorded in both the register link and the register while the pulses of the second and third digits are recorded in the register only and absorbed in the register link by the recording switch which takes but one step for each digit.

Another feature of the invention utilizes the setting of a switch in the register link in accordance with the digit pulses of the first digit to determine whether a trunk link or a local link is to be used in'the establishment of the connection. 7

Another feature employs the dial pulses of the first digit to determine whether the connection can be established through the final selector of the connecting local or trunk link directly or whetherthe final selector is to be used as a group selector to select a final selector associated with 30 Claims. (Cl. 179- 18) munity automatic telephone system provision" must be made for revertive calls. A feature of this invention provides a testmade bythe regis-= ter to determine if a selected busy lineis the same line" as the calling line. If such is the case, the register adjusts the register link so tha't reverting tone can be sent to the calling party to notify him that he is calling a party on the same line as his own and to hang up. The register link then proceeds to ring the called party andthe link disconnects all switches connected to I the line and talking battery is supplied from the line circuit.

A feature of this invention provides for the adjustment of the revertive impulse control circuit by means of which the register controls the I movement of the selector switches so that, on units selection, either battery or ground pulses are counted by the register depending upon the recording of an odd or even numbered units digit in the register.

The above mentioned and other featuresand objects of this invention and the mannerof .obtaining them will become more apparent and the invention will be best understood, by reference to the following description of an embodi.-.

ment of the invention taken in conjunction with the accompanyingdrawings which show. the register link and register circuits in detail andi the Fig. 2 shows the relation of the portions other circuits of the system to the :register link 1 and register circuits.

Fig. 3 shows the complete. registerolink cir- I cuit when Figs. 3a, 3b, 3c, 3d and 3e are placed together in accordance with Fig.6.

Fig. 4 shows the complete'register circuit when Figs. 4a, 4b and 4c are placed together as shown in Fig. 6.

Fig. 5 shows the terminal arrangement and numbering of the selector banks.

Fig. 6 shows how the portions of Figs.3 and 4 should be placed together.

For a more complete description of the opera-' tion of the entire system of which the register link and register are a part, reference is made 3 to the above mentioned co-pending patent application.

GENERAL Fig. 1 illustrates diagrammatically the system serving 200 lines. The well known 100-point power driven switch having seven brushes is employed as a register link line finder I06, a line finder H and a final selector II 2. A register link circuit I01 employs, in addition to the line finder I06, a rotary step-by-step switch I08 to select an idle register I09. Each local link circuit III has a line finder H0 and the final selector H2. All seven brushes are used on the line finder but only four of the brushes inthe final selector are used for calls within the 100 line group served by the associated local link. On calls to other hundred line groups theother three brushes and one of the first. four mentioned of the final selector are employed. Access to cult at final selectors of the trunk'link circuits.

II ,4' and I25 while. theother three serve for hunt- Ing purposes at theterminals of-the line finders U36. and H3.

The arrows in Fig. 1 indicate the direction of thecalls. For installations up to. 10.0 lines only.

the. line finders. I06, H0 and H3, the final selectorsII2 and H links I01, III and. H4, reg-.

ister selectors I08, registers I09 and two-way trunks I21 needbe provided in sufficient quantites to satisfy traific requirements. An installation, for 200 lines. does not require duplication of..all equipment but the lines of this group I03 needitheir own line finders H8, I2,I and=I24 and final selectors. I23 and I28, with appropriate local andtrlmk. links I22 and I25 and. registerlinks H8, which may be connected with. registers I09.

via. register selectors I20. It will be understood, oflcourse, that while200 lines have been referred to in this embodiment by wayiof. example, only, many more. 100 line groups. are. contemplated. Thetwoeway trunk circuits like I21are. accessible to all thegroups over the multiple. I3I. trunk circuits I21. terminate in conductors I30 onQthe banks of the'line. finders I06. and 'H3. They. require line numbers butno li'ne circuits.

The line numbers of the trunk circuitsv need not.

befconsecutive.

Whenthe subscriber I02 belongingto the200 line group calls, the line relay energizes the start circuit. I05 which starts the line findersi I06- of all. the idle register links I01servin'gthe200 group of lines and places test. potential on the test terminals of the register. link linefinders .I 0.6. The'line finders I05. ofathe. registenlinks likev I01 hunt together. and. when one findslthe calling line. theline cutoff relayis .energizedand. the

energizing condition is withdrawn from the; start circuit which removes the test potential from the test terminals. As soon as the line finder I06 of a register link I01'finds; the line, an' idle register l.09.,is seiectedby. the. r st r se ector. 0 n when the register is attached 0 he 1K "1 di toneis transmitted; from the link to the calling ine. 92.-

These dial pulses are repeated by a relay in the register link I01 not only to the register circuit I09 but to a rotary switch, called the link marker switch, in the register link I01. Impulses of the first digit position the link marker switch. The first digit dialed is the hundreds digit of a local line number or the single code digit for a trunk.

If the hundreds digit designates the same group of 100 lines, in which the calling line is located, threerelays are operated that adjust the link I01 to signal the register I00 that final selection is not to be made in accordance with the hundreds digit and the local link H0, III and I I2 is selectively operated to connect calling with the called line.

If the hundreds digit designates some other group, e. g. 300 line group, two of the three refrom g the. register link; I01. The 'calledfline is v tested by the register I09 which signals thereg ubscriber. n wdial the al We and; 5:.

lays areoperatedand the register is signaled to selectively operate the final selector H2 as a group selector to select the group of trunks in accordance with the hundreds digit and to hunt for an idle trunk I28 leading to a final selector in the desired line group. The selected final selector in this example would be one like I22 and it is then operated to select line I03 in the 300 line group.

If the hundreds. digit designates. anQunequipped group, the, -reg is ter link I01, releases.

and the line is locked out.

If a code is dialed,'another relay is operated which adjusts the register-link I01 to start line, finder I I3 of a trunk link I I4 and. to. use. the final selector H5 to hunt for an idle two .-.way.tri1nk circuit I21. i

' Allof theselectorsare controlled bythe -reg; ister on a local call. Thetens and unitsl digi are not registered in the'register link I0'1'but; he above mentioned link marker switch inlthe link. is arranged to move to position 9 afterthe first digit is dialed andthe above opera take. place. provided that digit signifies. ail al' line. Provision is made'fonrelease when the digit designates an unequipped' 100 linejgroup. "Th

positions 10 andll off the link markenswitch;

absorb the tens and-units. digits.

After the first digit ha's, been dialed, the line finders no of the idle locallin ks l l I er H305.

the trunk links I I4, designated by th sdia l ing of the first digitas above described are stanted andi one of them sei zle sthev calling line.

A fourth digit is, dialed. by ;cal-lirig*subr; scriber to select. thecalledstation i n aterr part ringing system. This. moves the link marker switch in the register link I01to a position for connecting the proper ringing current, to the link for ringingthe bell of the desired party.

Whenthe called subscriber answers, the reg-1.

ister link I01 is disconnected and the local linkv supplies battery for conversation. If' the called subscribers line isv busy, busy tone is supplied ister linkthat the. called line is busy oridl On an inward call the two-waytrunk I mission battery supply but theloperation is s f bf stantiallythe same as above.

Reverting calls should be recognized; by the.

calling party linesubscriber becausehe dials his own number followed by the, station digit fonthe,

desired party on his line. "However, busy n sent to the calling, partvand t i nh 10 15 15 i sf alal; Wh a i s-ist r:mi...

. i s i g.ea in I 10.7. tains ther eg ister link I01 and-the -dial pulse are calledline is the same as the calling line. A specialreverting tone-is then connected to the calling subscribers line and ringing is controlled in the register link I01, the local link I ll is disconnected when the called party answers and transmission batteryis supplied through the line and lockout relays and the register link I0! is disconnected.

DETAILED DESCRIPTION- -The attached drawings show the circuits for establishing the connections described above in general terms with reference to Fig. 1. Fig. 2 shows the apparatusof the line, local link, trunk link and'two-way trunk circuits with which the register link of Fig. 3 and the register of Fig. 4 cooperate inthe establishment of connections. The reference numbers are the same as shown in the above mentioned patent application to enable the tracing of the circuits. The con ductors to the ringing generator and various tone transformers and interrupters shown in Fig. 9 of the previously mentioned patent application aredesignated on Figs. 3 and 4 and theirpurpose is-givenin thefollowing description. The contacts of a given:relay are related by a fine line to the relay winding which controls .them.

The description is divided into sections as.

follows A--Local call to line of same line group-- 7 1'. Register link and register attached 2. Connection to register 3. Reception of the first digit 4. Local line finder attached 5. Reception of second and third digits 6. Tens selection '1. Units selection 8. Testing called line 9. Reception of ringing digit l r 10. Ringing the called subscriber, answer and release of connection I B-Local call to line in a diiferent line group- 1. Local line finder attached 2. Hundreds selection 3. Tens and Units selections 4. Test of called line ringing, answer and release C-Revertive call DOutgoing call to operator E--Incoming call from operator 1. Reception of the first, second and third digits Tens selection of a called line in the same hundreds group Units selection Test of called line Called line tests free Called line tests busy Ringing Call to a line in a different-line group FTime release ALoca.l call to line of same line grow? 1. REGISTER LINK AND REGISTER ATTACHED When the subscriber at station 200 raises his receiver from the switchhook, the line relay (not shown), associated with his line circuit is operated and connects battery through resistances 203 and 204 to relay 800 of Fig. 3. A test potential from battery through resistance 203 is connected to conductor 2l6.

.Referring to ,Fig. 3, relay 800 operates relay 302. Relay 802 closes the circuit over conductor 824 for starting the motor. Relay 803 operates slowly to allow time for the motor to get up to mane-new M full speed and drive the line finders of the free:

register links from theterminals, on which they are standing to enablesucceeding calls on the same line to obtain different line finders. I

Relay,802 closesv the circuits for the clutch magnets 30 8 of all free register link line finders, This circuit,

When test potential on conductor 216v is eh-,

countered by a brush 306, relay 3| l operates over its left hand winding in a circuit from battery, resistance 203 (see Fig. 2), conductor 2I6. brush 3236, contact of jack 332, back contacts of relays 346, 308 and 312, left hand winding of relay 3 to ground at a contact of relay 803. The operation of relay 3| i releases clutch magnet 308, and

connects ground from wiper 318 of the. link marker switch, contacts of relays 303, 309, and

310, front contact of relay 3| I, right hand wind-,

ing of relay 3| 1, contact of relay 312, winding of relay3l3 in parallel with the operatingwinding of relay 3! I. connects ground directly to the winding of relay M3.

The low resistance of the right hand winding of relay 3| l and the winding of relay 3l3 reduces the test potential on conductor 2l6 tosuch anextent that no other test relay 3!! can operate in parallel with the first relay 3 that operates. If a double test should occur, i. e. two line finders test the same line at the same time, there is insuflicient current to hold both relays 3 or to operate the relay 3I3. The first relay 3 to release removes its low resistancesliunt'allowing the other test relay 3| I to hold. The former circuit remains normal and waits for the next call. The operation of cutoff relay 205 operates the lookout and line relays, not shown, and battery through resistances 203 and 204 is disconnected from conductors 2l2 and H6. Relays-800, 802 and 803 release stopping all the other line finders.

2. CONNECTION To REGISTER When the brush 306 finds the calling line and resistance 403 (see Fig. 4) back contact of relay 300, wipers 43B, 409 and M2, in their normal positions, back contact of relay 400, make busy jack 444, conductor 313, when encountered by register.

selector wiper 325, back contacts of relays 333 and 326, a front contact of relay 3I2, left hand winding of relay 3! l, a front contact of relay M3 to ground, operates relay 3II.' The operation of relay 3 opens the circuit for stepping magnet 3!!! to stop the register selector. When the double test condition is satisfied as already-explained, and relay 3 holds, low resistance relay 3! cperates.

Relay 3 operates relay 326 and connects resistance 31! across the winding of relay 321 which operates. A front contact of relay 320, supplies ground for operating relay 328 through back contacts of relays 336, 335 andafront conv Relay 3i3 operates relay 312 which accesse- 7 tact; of-"I'felay 32-1 Relay 32$ operates relay 368' from greund; a fr'ont c'ontact' of; relay-326,back contacts of relays 335,- 333 ahd338, front contact" of relay'32'8g winding' of relay 3ll8 to battery. This ground "is extended through the front contactof relay- 3 28' to the left hand winding ofr'elay 326, resistance 3-19 to lock relay -32B.' The operation of relay 388" opens-the circuit of relay 3l'3 to brush 3% which'releases relays 3 I3, 3' 1 2 and consequently relays'3 l I and 344'. A contact of" relay 303" connects ground through resistance 355 to brush '3fl2,f con ductor 2I5 (see Fig-32), tie-operate relay2U5. This operatesth'e lockout relay; not -shown, in the line circuit, which disconnects battery'throug h resistance-203 from conductor" 2-1 3 atthe line" finder and from conductor 2 2 through resistance-2B4 toth'e's'tartcircuit (Fig.3)

Relay 3 26comp1etes a circuitfrom ground, a front-contact of relay 326 and a back contact of relay 349, left hand winding of relay 343, back" contact of relay 34 1 and 342; wiper 322 of the register selector, conductor 310, resistance 4!, winding of relay-433 to battery in the register circuit (Fig. 4). Resistance 4M prevents the operation of relay 343 at this time and relay wil o'perates. Relay 3G8'also connects the windingsofrelay-321 through the windings of tone transformer 315, brushes 300 and 30! to line conductors 2&3 and 2 14. calling subscriber by 1 tone coil 313* the primary winding 356 of which is connected to the dial tone transformer, not shown, conductor 388, wiper 31'! of the link marker switch, through back-contacts-of relays 334-a1id332 and a front 'c'o'ntact'of relay- 308.

The system is now ready to receive dial pulses.

3. RECEPTION.OF-ILHE' EI-RST DIG-IT Itis assumed that subscriber 200 makesa call "to a line in the same line group by dialing call :number 2341. As mentioned previously, the first digit dialed determines whether'a local or trunk If the local line is'one of the line of some other hundreds group, the final :sel'e'ctor associated with the local line finder is used as a group'selector and the-first digit dialed Dial tone is sent to the,

directs it to an idle trunk to a" final selector in r the desired h'undreds group. 111 eithercase a loca1'1ink is usedand the line finder thereof is connected to' the calling line by the register link; If' the first-dig itdialed designates an out-' going trunk call, a trunk link is used andthe register link receivesonly the one digit and mustbe' adjusted to selectively operate the final seshown in"solid"lin'es for the register links serv ing-theZOO' line group. Relay 33! is connected through aback contact" of relay 33ll'to terminal 2' and relay 330'is connected to terminal 3'. Forregister links'serving the 300 line group as shown by the dotted lines, relay 33l is connected to terminal 3 a'ndrelay 330 to'te'rminal 2. Since hundreds"numbers'4-to 9 inclusive are not assigned;.

these terminals: are connected together'and' to a back contact of relay 330: to short circuit the holdingi winuin'g: of relay 326' which releases;

When thisloccurs the registr link' is returnedto:

the dialing subscribers line" circuit is released.-

The lockout relay and the line relay, not shown} are connected to the line, remain operated and aguard groundis connected to conductors-215 and 226 until the subscriber releases. Digit 0 designates a trunk call and relay 333 is connected to terminal I D ot wiper 3H5 through a back contact of relay 332 to record. an outgoing calltothe operator as will be described in sectl OIl D;

The-subscriber, upon" hearing dial tone, commences to dial the assumed call number 2341. Relay 321 follows the dial pulses. Relay" 328 being slow to release, remains operate'd during" the train of impulses representing the digit. Each time relay 321 releases, ground fromafront'contact of relay 326, back contacts of re} lays 33G; 335'and-32 1, front contact ofrelay328. backcontacts ofr'elays 32land 331, winding of relay 329'in parallel with rectifier 351, back'con tactsoff relays 33-3 and 332, winding of magnet 3l5 of'thelink marker switch to battery. From the double "make contacts of relay 328 this gr'cundis also connected through back contacts of relaysi3-34 and34l, wiper 323 of the register selector, conductor 368, back contact of relay 440 in the register circuit, winding of relay 435, and rectifier 436 in parallel,v back contact of relay 438, windingofmagnet 403 of the hundreds marker switch. The'linkmarker switch and the hundreds marker switclr'in the register follow the dial pulses and" take two steps. Wipers 3l3, 3|! and 318 of the register selector stepto the second terminals. Relay 329' in'series'w-ith magnet 3I5 operates and holds while the pulses are being received.

At the end of the first digit, the position of the link marker switch corresponds to 'the' number dialed. Relay 329 releasesand connects ground from wiper 3I8'terminal 2; a front contact of relay 326, a back contact of relay 329', wiper 3|6 in position 2, back contactof rela'y- 330, winding of relay 33! to battery. Relay 33l operates and extends this ground to operate relay 330 and, through a back contact of relay 334-, tooperate relay 332. A contact of relay 330'locks'the-three relays to ground at a front contact ofrelay' 3261 The operation of relay 33A connects ground from a contact ofrelay 326- to wiper 32-l'of the register selector and over conductor 369, resistance B (see Fig. 4-), back contact of relay 445, front contact of relay 443 to operaterelay 43! in the register to cancelxg-roupselection when relay 443 operates after the hundredsi marker switch has been positioned: I'he operation of relay 332 completes acircuit fromi'ground', wiper 3 l8 of the link marker switch, contacts of relays 332 and 334;. wiper 311 and a contact of relay 332 to the interrupter contact ofmagnet 3l5 to step the link marker switch to position 9 as determined'b'y w'iper' 3 I 1 by self-interruption.

As previouslysta-ted the release of relay 321 sendsa pulse over wiper: 323' of the register selector't'o operate magnet 403 in'series with relay 435 and-acont'act of relay 438- in the register. The" t'wop'ul'ses. for the hundreds digit are recorded on the hundreds marker switch. Relay 435" operates on' the: first impulse and holds for the duration of the digit. When relay 435 releases at the end of-the pulses, ground from a back contact of relay: 431,.interrupter contact'of magnet 403 of the hundreds marker switch, back contacts of relays- 435 and 443, wiper 408 of the hundreds marker switch, a front contact of relay 400, normally closed contact and winding of relay-438 to battery, operates relay 433 which locks to a contact of relay 400. Relay 438 transfers the instepping circuit including series relay 435 from magnet 403 to 404 via a back contact of relay 439 and operates relay 443 to open the restoring circuit for the hundreds marker'switch and to operate relay 429 so as to allow selection to start immediately after the reception of the first digit, if required. This operation is coincident with the stepping of the link marker switch.

4. LOCAL LINE FINDER ATTACHED When relay 33!) operates, ground is connected to conductor 358 via back contact of relay 335, front contact of relay 330, back contacts of re lays 346, 339, 338, 333 and 335 and front contact of relay 326. This operates relay 805 (see Fig. 2) to connect test potential from battery, resistance 8|4, conductor 360, front contact of relay 330, back contacts of relays 335, 339, MI and 346, brush 305 of the link line finder, conductor 2l9, line finder brush 506 to operate relay 53l in the local link circuit 1 l I (see Fig. 2) when line finder brush 506 encounters this test potential. The line finder magnets 501 of the idle local links are energized when relay 805 operates from a ground via conductor 548. The details of this start circuit are not shown. Ground at a front contact of relay 326, back contacts of relays 335, 333 and 333, winding of relay 339, front contact of relay 308,

back contact of relay 346, contact of jack 362, brush 306 of the link linefinder, conductor 2l9, line finder brush 505 of the local link Ill (see Fig. 2) is connected to relay 533 which has been operated. Relay 339 operates in series with relay 533 and the line finder is now ready for the selective operation of the final selector.

5. RECEPTION OF SECOND AND THIRD DIGITS The calling subscriber proceeds to dial the tens and units digits while the line finder of the local link is being attached. The digits are recorded on the tens and units marker switches in the register and the link marker switch takes one step'for each digit.

When the subscriber dials the tens digit, relay 321 releases three times. Relay 329 operates in the previously described circuit to battery through resistance 364 and a contact of relay 332 and holds for the duration of the pulses. When relay 329 operates, ground from brush 318 and contacts of relays 329 and 332 operate the link marker switch magnet 3I5. When relay 329 releases, the magnet releases and steps the link marker switch to position 10.

In the register, the stepping circuit from the contacts of relay 321 via wiper 320 of the register selector and conductor 36!! operates relay 435 on the first impulse and by the operation and release of magnet 404, steps the tens marker switch to position 3. When the pulses cease, relay 435 releases and completes a circuit from ground, a back contact of relay 431, interrupter contact magnet 403, a back contact of relay 435, a front contact of relay 443, a back contact of relay 439, wiper 41 l ,'a front contact of relay 443 and a back contact and winding of relay 439 to battery.

Relay 439 operates and locks to ground from a releases, ground via wiper 3| 6 of the link marker switch in position 11 operates relay 334 which disconnect the stepping circuit from the register. Relay 332 releases to reconnect the link marker switch magnet .to relay 321.

When relay 435 in the stepping circuit of the register releases at the end of the units pulses, relayv 432 operates via brush 4I4 of the units marker switch and locks to ground from a contact of relay 400 to prepare the register circuit for units'selection.

- e. TEN;S SELECTION After reception of the first digit, the register link connects ground to wiper 32l of the register selector, operates relay 431 as described in section A3. Relay 43! opens the circuit of revertive pulse relay 429 and the fundamental ground ;to conductor 310 and wiper 323 to prevent operation of the final selector, removes ground from'terminal l2 of brush 408 of the hundreds marker switch, and completes a circuit from ground,=in terrupter contact of magnet 404, front contact of relay 431, interrupter contact of magnet 403, front contacts of relays 438 and 431,, wiper 408 of the hundreds marker switch, front contact of relay 43 I, back contact of relay 4l5, windingof magnet 403 to battery, to self-step the hundreds marker switch to position 12. This cancels the hundreds selection and prepares the circuit for tens selection. Relay 43l remains operatedfor sufficient time to insure the stepping of the hundredis marker switch. i

'The revertive impulse control circuit-is now closed from ground, a front contact of relay 400, wiper 406 and terminal l2 of the hundreds marker switch, front contact of relay 43 1, wiper 409, of the tens marker switch in position 3, back contact of relay 43l, front contact of relay 443, back contact of relay 445, conductor 311, wiper 323 of the register selector, back contacts of relays 34l, 349 and 346, front contacts of relays 339 and 326, brush 303 of the linkline-finder, conductor 2l1, line finder brush 503 of thelocal link, winding of relay 525 to battery. Relay 525 operates and extends this ground to the selector clutch magnet 5| 1 to rotate the selectors.

The numbering of the terminals in the selector banks for both the local and trunk links is shown on Fig. 6. These banks provide 51.positions including the normal position. As the :brushes revolve, one set contacts withone setof terminals on the first half revolution and the other set contacts with the other set of terminals, on the second half revolution. wThe-bank terminals are, in effect, divided :into two halves; an upper half, to which the subscribers lines and. 11100111. ing trunks are connected, and the lower-,half, to which the two-way outgoing trunks andthe trunks to other hundreds groups-are connected. The test terminals are located between two halves. It will be noted that the terminals arenumbered down beginning at the. left, or with the movement of the brushes. This numbering arrangement makes it possible to step the wipers of'the digits marker switches forward a number .01 steps which is the tens complement of the position, in which the wipers are set'by the dial pulses, i. e., the digit dialed. V

For examplaif a number 3 is, recorded by dial pulses on one of the digits marker switches the switch will thentake 7 steps under controlof the revertive impulse circuit which will drive the brushes of the selector, asshown on Fig. 5; to the terminals numbered 3. More specifically; a brush identified as 5l6 -6l6 is driven over the 0, 9, 8, '7, -6, trunk groups and :the -mate zbrush 5|5-'-6t6 is driven over the 5 :and .4: trunk groups to the first terminal .of trunk group. 3. Similarly, the case of a line, the brush is driven to the terminal by a number .of :steps which is the tens complement of the terminal. !l hus,;brush 5 l 6 lll ifline 53 :is to be selected, is dr'iven'l positions'to line terminal 253 having been broug'ht to :restron terminal '50 :by :the "tens selection.

Referring to Fig. 2, as the selector .brushes rotate, ground iromcontacts .I, ll, 2|, etc., brush 516, through the local link circuit, local line finder "brush 504, conductor F218, linkline :finder brush .front contact-of relay 339, back contacts o'tcutlays 1342, 346, 349 and 34'I,--wiper -324 of the register selector, conductor 312, back contacts of -relaysifl and 430, winding of relay -429, back contacts-of relays-430:and' 43l', :a front contact creamy-1'43, resistance-1'42 to battery, operates aelay -lzflof the register circuit. Ground from the-Trent -.contact ofrelay- 42 9- operates .magnet 4040i the *tens marker switch via a back: conof- :relay. H5, wipe-r 441 position .12 I of :the hundreds marker switch, front contact-of relay 43 1," magnet4fl4 to battery. Relay 433 is also operated thisjcircuitand looks from ground, 'interruptercontact :of-.magnet 404, front: contact ofrelay 431, interrupter contact o'f'magnet 403 -and front contacts of relays 43B and 433 to-insure that m-ag net 404 will :take :one step 'for each 'revertivepulse, however short, is received.

In this illustration the tens marker switch was setzin-position3 by the dial pulses. When "the tens marker switch reachesposition 110' after taking 7 steps, ground from a contact of relay 4011, wiper .406 of the hundreds marker switch p'o's'iti'on 12,-- a. front contact, of relay .431, wiper :409 of the tenslmarker switch position'lO, windingpfrelay- 428 to battery, operates relay 426..

'At *this time :brush 516 is -moving from group A ter group 3, i. .e., "from test terminal 6|: to. 1| Tsee Fig. '5); Ground is maintained on .the fundamerital circuit over conductor 3TH attheback {contact of relay-i429" to hold relay 525 and mag- :net' 5'l4 fin the locallink. On the next operation of relay 429; magnet 4 is energized andrelay 4 l6"'-is::operated througha front contact of relay IZB -anda 'b'ack contact ofrelay 4L5. Relay 5.25 and" magnet 5H release and 'stop the selector 'brushes attest terminalll corresponding to line terminal "311 (see Fig. "5). Relay 445 operates from acontact of relay4l5 and opens the circuit from wiper 324 via conductor '3' of the reg-isterselector to release relay-429. The release oft-relay 429 de-energizes magnet 404 stopping -the'tens marker switch in position 11 and opens the circuit for relay 416. When the tens marker switch steps-to position 11, relay 428 is released and a" short time later relays 4| 6 and-4 I5 release in turn. The register circuit is then prepared for units selection. r

' V '7. UNITY-SBELECTION Whenan odd number .is'dialed for the units digit, the units marker .switch is stepped to an odd-numbered position and ground from a contact-of relay 40.0,, .wiper 4 06 position 12 of the hundreds marker switch, .iront .contact :of, .relay 431, wiper 410 position 11 of the tens marker :switch, front contact of relay 432, wiper .412 of .the imifis marker switch'operates relay' 430 which locks .to groundat a contact ofrelay 400. Relay .430; transfers the operating circuit for relay 429 to respond to .revertive battery pulses for .odd number unit digit selection. For even numbered units ldigits, relay 4.39 :does. .notcoperate and; relay 42.9 responds ito;rever.tive ground pulses.

.The release of relay 4:45v at the end of ten-s selection again connects ground to wiper 323 of the register; selector; and ingthis example responds to :revertive ground pulses since the units digit dialed is 4 and the. units marker switch isin position: 4.. The revertiveimpulse control circuit isxnow closedzto conductor .z2l'l :and, relay 55255 and :selector clutch magnet .511 of the local link ILI (see ,Eig. 2;) .are againgoperated and .the selector brushes rotate. .IAS. the, selector rotates, revertivehattery pulses from. selector brush 5H3, line finder'brush 586, and conductor 'ZI'B operate relay-429.

Thetens marker switch is again stepped *by relay 4Z9-until relay 44U'isoperated. 'Ma'gnet4ii'4 operates from ground, front contact of rela '42'3 and back-contact of relay-415, wiper 401 in position 12' of the hundreds marker switch, 'front contact of relay '43l magnet 4D4to battery. Relay -'440 operates from ground, a front contact of relay 400, wiper'406 in position 12 of the hundreds marker switch, front contact of relay 431, wiper 4H] in position 14, in this example, of the tens marker switch, wiper-413 inposition 4 of the units marker'switch, winding of relay 446 to battery. The operation of relay 44ll 'connects ground, front contact of relay 400, wiper 406 position 12, front contact of relay 431, wiper- 449- positions l-115, a f-ro'nt contact-of relay "449, to operate relay 423 and places the fundamental ground under'con- =trol of relay 429 because ground remains con- =nected"to conductor 31 l from back contacts of gelays' 429 and 431 and a front contact of relay Ground from frontcontacts of relays 41mand Miland a back contact-of relay 4 l 5 operates relay 4|! which connects ground via back contacts of relays :41 9 and 42.6 to the winding of slow operating relay 424. The next operation of relay 429 from ground-on brush .5 llfiof the selector removes ground from conductory3l'l to release relay 52,5 andimagnet, 5 I I and stop the selector. Relay 429 operatesrelay M6 via .a from; contact of relay 428. Relay 415 operates relay 445 in an obvious circuit and releasesrelay 42 9,;closes a circuitfrom ground, winding of relay "422, back contacts of relays'42t and M9, front contacts of .relays 44,0 and 445 to conductor .312 for testing thebusy-or idle .condition of the called subscribers.line,..and connects ground via resistance 441 and front contacts, of relays 44.0 and 44.5 to conductor 3?! for operating .relay .525 but notmagnet 5H of the final selector. Relay 445 locks to ground at a Iront contact of rela 4H. Therelease of relay 429 releases relay 4 I6.

8. TESTING CALLED L'INE When the final selector arrives at the terminals of a free non-P. B. X line, cutofi relay 205 is connected-to relay 42 2v of the register via conductor, 226, final selector brush M2 and finder brush 5.0.4 of the local link, .conductor .2 l8, finder brush 3.44 of, the register link, wiper 324 of the register selector, conductor 312, front contacts of relays 445,440, a back contact of relay 41,9 and winding of relay 422 to ground. Relays 205 and 422 operatein series.

'As previously described, when relay 4!! in the register circuit was operated at the endofunits selection, a circuit was closed for the, slow. operating .relay 424. The operation of relay 422 .oper- .ates.relays 423 and 42.0 in turn. Whenrelay 4.24 operates after. a time, resistance 401 is short cirvia conductor 364.

resistance ground which prevents relay 422 from operating so that when the'slow operating relay 424 finally operates, ground isconnected from back contacts of relays 426 and 420, front contacts of relays 424 and 443, conductor 338,}wiper 320"of'the register selector, back contactof relay 341, front contacts of relays'334 and 333, back contacts of; relays 342 and 341, winding of relay 342 to "battery in the register circuit. Relay342 operates to record the busycondition and'to open the circuit to the holding relay 433 via wiper- 322 causing the register circuit to restore, 1 I I fWhen' relay 400 'releases the general holding ground for the-regi'ster is removed'and all relays release. The units marker switch is restored to normal from ground interrupter contact ofm'a' net 405, a back contact of relay 438, wiper 414, back contact of relay 431, winding of magnet'435 to battery.- The units marker switch self-steps until the wipers are in their normal position when i this circuit is opened.

' The tens marker switch restores from ground, interrupter contact of magnet 404, back contacts of relays 431 and 438, wiper 411, back contact of relay 443, winding of magnet 434 to battery. The

magnet self-steps in this circuit' until the Wipers resistance 433, wipers 436, 403 and 412 in their normal positions, back contact of relay 405, contact of jack 444, to conductor 313'. Until thiscircult is restored the register is unavailable.

I f the called line is the first line of a P. B. X

group, and is busy, the inductive windingof the cutoff 'relay 205 is shunted by a resistance, not

shown, 'When the held line is busy because of a resistanceco'nnected to ground in a local or trunk link, there will be-sufficient test potential to operatefrelay 422 and relays 423 and 423 operate in turmf iRelay 420 removes the short circuit on 'resistance421, causing relay 422 to release; The

release of relay 422 connectfi ground, contactsoi relay-e423, 422, front contacts of relay 420 and aback contact of relay 4 26; windingoi relay 419 to battery and releases relays 423 and 423. The

operation of relay 419 opens the operating circuit of relay 424. The release of relay 423 operates relay 423 from a contact of relay 413. Relay 426 connects direct ground to relay 52 5 .and clutch magnet 5 11 of the local link (see Fig. 2), via back contacts of relays 423, 422 and 430, a front contact of relay 423, back contact of relay 421, front contacts, of relays, 440 and 445, conductor 311, wiper 323 of the register selectonthrough the register link circuit, brush 30-3 or the register link line finder, conductor 211, brush 533 of the local line finder to operate relay .525 in the local link. When a free P. B. X line is encountered, relay icuitv holds until the subscriber releases.

1.4 422 operates via conductor 312, wiper 324 of the register selector and brush 512 of the-selector in the previously described circuit, operates relays 423 and 420 and opens the ground circuit to relay 525 and clutch magnet 511 of thesele'ctor. The operation of relay 423 closes the operating circuit for relay 424, via relays 42B and 411. When relay-424 operates, a free line signal is sent to the register link and the register is restored as previously described.

If no line of the P. B. X group is free, sufiicient test potential'is connected to wiper 324 of the register'selector, when the last line of the group is reached, to operate relay 422 because the cutoff relay 205 of the last line of a P. B. X group "is shunted by a resistance the same as the first line of the group. Relays 423 and'420'operate'in turn and; if the line is busy, relay 422 releases when the operation of relay 420 insertsresistance 421 in series with the windingof relay 422. The

operating'circuit for relay 424 is completed by relay 420. Relay 421 then operates from ground via, contacts of'relays, back contacts of relays, back contacts of relays 429 and 422 and front contacts of relays 420 and 426. Relays 423 and 4211' release after a short delay. The operation of relay 421 closes the operating circuit of relay 42 4.- The operation of relay 42'4 connects ground via front contacts of relays 421, 424 and 440, conductor 368 to wiper 320 of the register selector to signal to the register link that all P. B. X lines are busy.

When a line busy signalis received in the register link by ground via wiper 320 of the register selector, relay 342 operates as previously described and locks to ground via a back contact of relay 349 and a front contact of relay 325. Relay 342' opens the register holding circuit via wiper 322 of the register selector thereby releasing'the register, operates relay 341 which opens connections to the register and connects relay 348 to brush 304 of the link line'finder via front contacts of relays 331, 331, 342, and 339. Relay 348 operates in parallel with the grounded resistance of the local or trunk link. In th register link circuit that receives the line busy signal, relay 348 connected to link line finder brush 304 as previously described-is connected via conductor 218, local line'finder brush 504 to brush 512 which at that time is connected to conductor 22B, Relay 341 operates via front contacts of relays 343 and 342, back contact of relay 349 and front contact or relay 326' to ground and locks. Since this is not a revertive call relay 348 remains operated. Relay 342 releasesslowly from a contact of relay 341. Busy tone from the busy tone transformer, not shown, conductor 333, a back contact of relay 303, front contacts of relays 341 and 331 to the primary winding 353 of tone coil 318is sent to the calling subscriber. The cir- When that occurs, relay 321 releases, releasing, in turn, relay 323. Relays 323 and 3138 release removing the general holding ground. The marker switch restores'from ground, wiper 318, back contacts of relay 326, interrupter contact and winding of magnet 315'to batteryafter relay 326 releases leaving the register'link circuit normal.

7 .9. RECEPTION or R'INI'IGING nierr After thev unitsdigit has been recorded as described in section A-5, the ringing digit is recorded only in the register link'in the same manner as for the hundreds digit as described in section 3 except that'the link marker switch starts from position 11. .marker switch proceeds .while the register is selecting and testing the *called lines as :described .in sections'A-G, A4 and .A-8. Relay=329oper .This operation of the link ates .and .holds during the :series 'of impulses. The link marker switch steps to aap'osition from .12 ;to 21 dependingon 'the number dialed. .This

,providesfor. lines with amaximumof ten parties t-and .full selective ringing. .Five-lringing fre- .Relay'312 operatesfoncodes 6 to 10 .totransfer .ringing current from line wire 224'to1line wire I225. Brush "304 of the link line. finder, is con- 'nected-viaconductor'218-.-to brush 04 ofthe local line .finder, through the local :link circuit (see Fig. 2) :to selector brush511and-line conductor .225. Link .line finderbrush-303 is connected via "conductor 21 1, local line finder brush. 503, through the local link circuit (see Fi 2) toselector brush 5 I 0 and line conductor 22 4.

Ringing current from the harmonic :ringing conductors 900, wiper 31-1 of the link marker switch, front contact of relay 331, winding of relay 338, contact of relay 312, and when the relay'is notoperated through a back contact of thatrelay afront contact-of relay 349, back contact of relay 3'46, aback :contact of. relay 342, a front contact of relay 339 to link line finder-brush 304. When :relay 312 is operated the Winding ofrelay 338 is then connected -via a frontcontact-of relay 31-2, a irontcontactof relay 349, a .back contact'of relay 346, front contactsof relays 339wand 326 :to link lineflnder brush 303. The ground return for the ringing circuit may be traced .through wiper 318 of thelinkimarker switch position .12 to 21 which connects ground .to link line finder-brushes304 or-303 depending upon the position of the switch. For example, when relay 31 2 is :operated Wiper :318is in :a ,po-

sition from 17 to 21am ground is connected over the :front contact of relay 349 to brush 304, the ringing current from wiper 3 I 1 being at=-that time connected in series with the winding of .relay 338 to link line finder brush303. The circuit waits until selection is complete'and a free or busy signal is received from theregisteras described .insectionA-B.

The following table- .willclarify the ringing conditions of the +party harmonic ringing system.

1'0. R'INGIN'G 'THE' CALLED' SUBSCRIBER. A'NSWVER AND RELEASEOF CONNECTION If the .called line. tests free, the register sends a line free signal to the register link and relay 343 operates when ground is removed from the pickup conductor 364 at the beginning of the ringing period. This allowsrelay 343 tooperate at'the proper time :ior code ringing, if used, so that the correct number ofirings is sent .out'whe'n the ringing first: starts. Relay 343 operates-relays 349 and 341 and connects battery through resist.- ance 344,.a front contact of relay 343, a back 'contactof relay 346, link line finder brush 30.5 to conductor 219. The holding relay 525 in the local link circuit is operated but the magnet 51 '1. is not. This causes the local link circuit to cut through for ringing. Relay 349 connects the .ringing trip relay 338 to the appropriate side of the line and connects ringing tone over conductor 384, front contact of relay 349, back contact of relay 341, front contact of relay 426, primary winding 356 of tone coil 318 to the callingline,

When the called subscriber answers, the line loop is closed, operating the ringing trip relay 338 from batteryin theringing source and ground .on brush 310 of the link marker switch. .Relay 338 releases relays 308 and 326. Relay 308. removes the-generalholding ground for the register link and the remaining relays release. The link marker switch is self-stepped to normal from ground, wiper 318, back contacts f relay 326-, in-

terrupter contact and winding of magnet 315 to battery, thereby returning the register link to normal until another callis originated.

When the ringing is tripped the register link opens the'circuit over conductor 216 to place the local link in the talking condition. The line finder brushes are connected through a bridged impedance type transmission circuit to the final brushes of the local link and the connection is placed under control of the calling and called subscribers.

When the calling subscriber disconnects the local link 111 is released and restores to normal. .If the called subscriber has not disconnected therelease of the cutofi relay of the called line "will .place the line circuit in the lockout condition until he disconnects.

B.Local call to line in a difierent Zinegroup When the subscriber at station 200 wishes to call a subscriber in a different hundreds group, the operations described in section A-1 and A-2 attach a register link to the calling line and a register to the link and the system is now ready to receive dial pulses. It is assumed that line number 3341 is called.

1, LOCAL LINE FINDER ATTACHED As described in section A-3 the dial pulses step the link marker switch in the register link circuit and thehundreds marker switch in the register to'their position 3. When relay 329 releases, relays 330 and 332 operate via wiper 316 of the link marker switch. Relay 331 is not operated indicating that the call is for a line in a different group and relay 431 of the register circuit isnot operated at this time.

A local link is attached as described in section A-4. When it is attached and before relay 339 operates, ground from wiper 318 of the link marker switch, front contacts of relays 332, back contacts of relays 331 and 339, brush 304 of the link line finder, conductor 218 and'brush 504 of the local link line finder operates relay 530. '(see Fig. 2). The operation of relay 530 transfers the link connections from brushes 5| 0 and 51 I to brushes 513 and 514, opens the circuit to brush 512 and connects brush 515 to the circuit of the selector, thus utilizing the terminals of the lower half of the selector ar'c.

2. HUNDRED S SELECTION After the first digit is recorded, the local line finder is :attached and relay- 339 is operated, the

register proceeds with hundreds'selectlon and the final selector of'the local link is operatedas a group selector. Ground from a front contact of relay 400, wiper 406 in position3 of the hundreds marker switch, back contact of relay 431, front'contact of relay 443, back contact of relay -445, conductor 3'11, wiper 323 of the register selector, back contactsof relays 341, 349, 346, front contacts of relays 339 and 326, brush 303 of the link line finder, conductor 2, brush 503 of the local line finder, operates relay 525 and clutch magnet 511 which rotates the group selector.

rotate from ground via back contacts of relays 429 and 431 which holdsrelay 525 operated until the next revertive pulse is received and relay 429 The group selector is stopped'on the operates first line of the correct group by the operation of relay 429 which operates relay 416. Relay 445 operates and opens the circuit for relay 429 which releases allowing the hundreds marker switch tostep to positionjll- H 1 When the hundreds'marker switch reaches position 11, relay 415 operates and both relays 415 and 445 lock to wiper406 in position 11 of the hundreds marker switch. .Re lays 428 and 416 release. nects ground, winding of "relay 42-2, back contacts of relays ,420 and419, front contact of relay 4'15, conductor 369, ."wiper-321 of the register selector, back contact'of' relay 331, front contact of relay 339, back contacts of relays 341 and 346, brush 305 of the lin'k'line findereconductor 219, brush 506 of the local line{ finder to brush'515 of the group selector. Ground from back contactsof relays 429, 422 and 4 20, front contact of relay J41 5,'conductor 3'1.1 wiper-323 of the register selector, back 'contacts'of relays 341, 349 and 346, front contacts of relays 339 and 326, brush 303 of .the' link line finder, conductor 211, brush 503 of the local line finder, operates relay 525 and magnet 51'! of the local. link. Relay 415 alsocloses'. a circuit for operating relay 431 from ground, a back contact of relay 431, front contact'of relay 415, a back contact of relay 424 and a front contact of relay 443. Relay 415 alsoconnects the ground from the back contact of relay 431 through back contacts' of relays 419' and 426 to operate relay 424. -Relay 424 is a slow operating relay, relay 431 opens the operating circuit for relay 429 to allow sufilcient time for the se-' lector to rotate from the first-trunk position if th'etrunkisbusyp If the first trunk of the selected group is free, relay 422 operates in series with relay 540' of The operation of relay 415 con- 1 l8 releases and removes ground from magnet 403 of the hundreds marker switch. The marker switch then steps to position 12 and releases relays 445, 515 and 431. Relay 424 operates and short circuits resistance 401 in series with conductor 3'10 and wiper 322 of the register selector to give the register link a free line signal. This signal is ignored by the register link because the operating winding of relay 343is short circuited at this time. 1

The operation of relay 422 removes a short circuit on resistance 425 to prevent clutch magnet 511 from opening and relay 525 operates to connect ground to selector brush 515 to hold relay 540 in the selected final-selector and mark the connecting trunk as busy.

If the first trunk of a group is busy, relay 422 does not operate when the trunk is tested. The group selector is rotated by the operation of relay 525 and clutch magnet 511 from ground via relays 429, 422, 423 and 445 of the register circuit. The group selector will rotate until a free trunk is found and relay 422 operates.

Relay 424 which operates slowly, will operate before the last trunk is reached and open the operating circuit for relay 431. The release of relay 431 closes the operating circuit of relay 429. The selector rotates to the first trunk of the next trunk group and relay 429 operates from ground on selector brush 516 through a previously described circuit. The operation of relay 429 removes ground from selector clutch magnet 51 1 and relay 525 to stop the rotation of the group selector. Relay 429 operates relay 440 which connects ground via relays 426, 420 and 424, conductor 368, wiper 420 of the register selector to operate relay 342 to release the register as previously described in section A-8 for a line busy signal.

'3. TENS AND UNITS SELECTIONS The reception of the second and third digits by the tens and units marker switches and counted by the link marker switch proceeds as described in section A-5.

Connections at this time have been established from the register, via a register link and a local link in which the final selector, functioning as a group selector connects line finder brushes 503 and 504 via selector brushes 514 and 515 respectively, to trunk conductors 544,545 and 546 incoming to a. selected final selector in the difi'erent group. Ground from a contact of relay 539 via selector brush 515, conductor 545v of the trunk from the group selectorto thefinal selector of the selected final selector via brush 515 and con-1 ductor 545, winding of relay 540" to battery, and opens the ground circuit to relay 525 and clutch magnet 511 of the selector circuit to stop the rotation of the selector. The operation of relay 422 connects ground from a back'contact of relay 429, a front contact of relay 422, a frontcontact of relay'415, wiper 401 to magnet 403 of the hun- 422 also operates redreds marker switch. Relay lays 423-and 420in'turnu1 I V a The operation of relay 420; inserts resistance 421'in series with the'winding of relay 422 which the different group, operates relay 540' of the final selector. r

The reference numbers that are primed refer to the final selector of the different group which is connected to the group selector over trunk conductors 543,544 and 545.

The final selector circuit of the different link operates essentially in the same manner as described in sections A-6 and A-1 except that the operation of the selector clutch magnet 511 and relay 525' is controlled over conductor 543 instead of finder brush 503 and revertive pulsesfor' the positioning of the selector are transmitted over conductor 544 instead of finder brush 505.

AQTEST OF CALLED LINE RINGING, ANSWER AND RELEASE 

